We report here the fabrication and characterization of GaAs tunnel diode (TD) and ErAs nanoparticles (Nps) enhanced GaAs TD. Four GaAs TDs with different contact area were fabricated by using MOCVD. We found extremely high peak current density of ∼250A/cm2 for the TD with r=0.25mm contact area. Moreover a hysteresis loop was appeared during sweeping up and sweeping down the external voltage. A ‘vector load line model’ was proposed to explain the origin of the shape of the hysteresis loop and the onset of the bistability occurred at the intersect of the loadline and the current-voltage (I-V) curve of TD. Meanwhile, we have grown ErAs Nps on GaAs(100) surface by using MBE and succeeded in overgrowth of GaAs after ErAs deposition. GaAs(p+)/ErAs(Nps)/GaAs(n+) TDs were fabricated and characterized. We found the GaAs sample containing 70s deposition of ErAs showed the best TD behavior. No TD behavior was observed for the sample without addition of ErAs Nps, clearly indicating the strong tunneling enhancement effect from ErAs Nps.

We have fabricated GaAs/GaNAs and GaAs/GaNAs/InGaAs MQWs introduced into the intrinsic region of GaAs p-i-n solar cells by atomic H-assisted RF-molecular beam epitaxy. Compared to the more conventional GaAs/InGaAs MQW cells, GaAs/GaNAs/InGaAs MQW cells exhibited improved external quantum efficiencies in the low energy region. This is due to the extension of band edge into longer wavelengths as achieved by use of GaNAs materials.

The effect of growth temperature on the crystal quality and optical properties of Ga(In)NAs films was investigated over a range of 340 ∼ 520 °C. We found that Ga(In)NAs films fabricated at lower growth temperatures generally result in an improved crystal quality. An XRD linewidth of as low as 45 arcsec was obtained for a 1 µm-thick Ga0.94In0.06N0.01As0.99 thin film grown at 380 °C. This is ∼1/2 of that grown at the conventionally-adopted growth temperature of 480 °C. After annealing, an improved optical property represented by a higher PL intensity compared to the conventional growth method (annealed, Tgrowth = 480 °C) was also obtained in the 1 µm-thick Ga0.94In0.06N0.01As0.99 thin film grown at low temperature of 380 °C.

We have studied the effect of strain compensation in multiple stacking of InAs self-assembled quantum dots on GaAs (001) substrates grown by atomic hydrogen assisted RF-molecular beam epitaxy. The GaNxAs1−x material was used as a strain compensating spacer layer. We confirmed by high resolution x-ray diffraction measurements that a 40 nm GaN0.005As0.995 strain compensating layer provides compressive strain to compensate for tensile strain induced by 2.0 ML InAs quantum dots. Consequently, we achieved a multiple stack of InAs QDs up to 30 layers without formation of coalesced QDs, and the density of QDs exceeded 1012 cm−2.

We have evaluated the photoluminescence (PL) properties of quantum dots (QDs) embedded in a p-n junction on GaAs(311)B and were compared with the identical structure grown on GaAs(001). The QDs on these two surfaces were fabricated with a similar size and density by optimizing the growth conditions. The PL emission from the QDs grown on GaAs(001) rapidly disappeared when the excitation power was decreased below 0.4W/cm2, while that from on GaAs(311)B was clearly observable even at a lower excitation power of 0.1W/cm2. From the measurements of PL intensity dependence on temperature and applied electric field, it was found that there are clear differences between the QDs grown on (001) and the QDs grown on (311)B in the recombination rates through non-radiative processes and/or the escape rates of carriers out of QDs to the GaAs host through a tunneling process.

The transition temperature Tc for the AlAs growth to change from/to a nucleation mode and step-flow mode have been studied on vicinal GaAs substrates (A-surface and B-surface) in molecular beam epitaxy (MBE) and atomic hydrogen-assisted MBE (H-MBE) using reflection high-energy electron diffraction (RHEED). The lowering of Tc was clearly observed in H-MBE compared to conventional MBE. For growth of AlAs on vicinal GaAs substrate in H-MBE, atomic H is thought to promote not only the re-evaporation of Al adatoms on the terrace, but also the incorporation of Al at the step edges, thereby facilitating a step-flow growth mode at a lower temperature than in MBE. The differences in the fundamental growth mode between on A-surface and B-surface have also been studies based on the differences in the atomic structure between the two substrates.

The purpose of this work is to achieve a high-quality epitaxy of GaAs-on-Ge system at low growth temperatures of 300 ∼ 400°C, by atomic hydrogen-assisted molecular beam epitaxy (H-MBE), in attempt to reduce Ge segregation to a minimum and to realize a layer-by-layer two-dimensional (2D) growth mode from the initial stages of the growth. A high-quality heteroepitaxy is expected in H-MBE technique as atomic H is known to act as an effective surfactant modifying the kinetics and energetics of the growth, which are practically difficult to control on atomic-scale unless a third element like a surfactant is introduced into the growth system. It is shown with the support of reflection high-energy electron diffraction (RHEED), secondary ion mass spectroscopy (SIMS), and atomic force microscopy (AFM) characterization that an enhanced layer-by-layer 2D growth can actually be realized and (2×4) GaAs(001) surface can be achieved in low-temperature heteroepitaxy on vicinal Ge(001) substrates at 400 °C by H-MBE.

A new concept of thin film growth/regrowth process design taking atomic motions into account using molecular dynamics is proposed. In the system, a modified many-body Tersoff-type interatomic potential for silicon has been adopted. The mathematical derivation of higher order derivatives was rigorously treated. Among many applications, the solid phase growth process was studied. It has been found from simulation studies that the solid phase growth of crystalline silicon proceeded along the [110] direction layer by layer. Furthermore, it has been obtained that all the atoms are activated in an extremely thin amorphous silicon film. Based on simulated results, an experiment using an extremely thin amorphous silicon film was carried out. It has been found that the perfect spherical silicon crystals with a uniform size and spacing can be grown from a thin amorphous silicon film.